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Longest Common Prefix

Certification: Basic Level Accuracy: 100% Submissions: 2 Points: 5

Write a Java program to find the longest common prefix string amongst an array of strings. If there is no common prefix, return an empty string "".

Example 1
     
  • Input: strs = ["flower", "flow", "flight"]
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  • Output: "fl"
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  • Explanation: 
       
    • Step 1: Take the first string as the initial prefix candidate.
      •  
    • Step 2: Compare this prefix with each subsequent string in the array.
      •  
    • Step 3: If a string doesn't start with the current prefix, reduce the prefix length until it matches.
      •  
    • Step 4: After comparing with all strings, "fl" is the longest common prefix.
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    •
Example 2
     
  • Input: strs = ["dog", "racecar", "car"]
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  • Output: ""
    •  
  • Explanation: 
       
    • Step 1: Take "dog" as the initial prefix candidate.
      •  
    • Step 2: Compare with "racecar" - there is no common prefix since 'd' != 'r'.
      •  
    • Step 3: Since there's no common prefix at the very first position, the result is an empty string.
      •  
    • Step 4: Return an empty string as the longest common prefix.
      •  
    •
Constraints
     
  • 1 ≤ strs.length ≤ 200
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  • 0 ≤ strs[i].length ≤ 200
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  • strs[i] consists of only lowercase English letters
    •  
  • Time Complexity: O(S) where S is the sum of all characters in all strings
    •  
  • Space Complexity: O(1)
    •
StringsTech MahindraDropbox
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Hint
Solution

Solution Hints

    
  
  • Start by assuming the first string is the common prefix
    • 
  
  • Iterate through the rest of the strings and compare with the current prefix
    • 
  
  • If a string doesn't start with the current prefix, shorten the prefix
    • 
  
  • Continue until you find a common prefix or determine there isn't one
    • 
  
  • You can implement this using either horizontal or vertical scanning approaches
    •

Steps to solve by this approach:

 Step 1: Check if the input array is null or empty. If so, return an empty string.
 Step 2: Take the first string in the array as the initial prefix.
 Step 3: Iterate through the remaining strings in the array.
 Step 4: For each string, check if it starts with the current prefix.
 Step 5: If it doesn't, repeatedly shorten the prefix by removing the last character until the string starts with the prefix or the prefix becomes empty.
 Step 6: If the prefix becomes empty at any point, return an empty string as there is no common prefix.
 Step 7: After processing all strings, return the final prefix, which is the longest common prefix among all strings.

Submitted Code :